JP4258542B2 - Optical disc apparatus and objective lens type discrimination method - Google Patents

Description

  The present invention relates to an optical disc apparatus that includes a plurality of objective lenses in an optical pickup and switches the objective lens according to the type of optical recording medium, and more particularly to an optical disc apparatus configured to prevent erroneous setting of the objective lens. The present invention also relates to a method for discriminating the type of objective lens of an optical pickup that switches between a plurality of objective lenses.

  Optical recording media such as compact discs (hereinafter referred to as CDs) and digital versatile discs (hereinafter referred to as DVDs) are widely used. Furthermore, in recent years, in order to increase the amount of information in an optical recording medium, research on increasing the density of the optical recording medium has been promoted. For example, a high-density optical recording medium such as a Blu-ray disc (hereinafter referred to as BD) is also practical. It is becoming.

  An optical disc apparatus that performs recording / reproduction of such an optical recording medium is provided with an optical pickup capable of recording information and reading information by irradiating the optical recording medium with a light beam, depending on the type of the optical recording medium. The numerical aperture (NA) of the objective lens used in the optical pickup and the wavelength of the light source are different. For example, the objective lens NA is 0.50 and the light source wavelength is 780 nm for CD, the objective lens NA is 0.65 for DVD, the light source wavelength is 650 nm, and the objective lens NA is for BD. NA is 0.85, and the wavelength of the light source is 405 nm.

  As described above, since the NA and wavelength of the objective lens used are different depending on the type of the optical recording medium, it may be possible to use different optical pickups for each optical recording medium. Since there is a problem such as an increase in size, it is general that a single optical pickup can read information on a plurality of types of optical recording media.

  Among optical pickups that can handle a plurality of types of optical recording media, for example, there are optical pickups that are configured with one objective lens for three types of optical recording media such as CD, DVD, and BD. Such an objective lens is difficult to design and may increase costs. For example, a BD objective lens that requires a high NA and a CD and DVD objective lens are separated into a plurality of types. There is also an optical pickup that switches between lenses for use.

  By the way, in the case of an optical disk apparatus that uses a plurality of types of objective lenses by switching, the objective lenses are generally switched by using a permanent magnet and an electromagnet to generate a kick pulse in the electromagnet so as to repel the permanent magnet. The method of switching the objective lens is adopted. However, when such a method is used, there is a case where the objective lens rebounds because the momentum at the time of switching is too strong and the objective lens is not switched. Moreover, a member that supports the objective lens may move due to a large gravitational acceleration from the outside due to a certain time signature, and the objective lens in the optical path may be replaced with an original one.

  And, when the objective lens in the optical path is different from the original one, if you try to reproduce the information on the optical recording medium or record the information on the optical recording medium, the information is not reproduced or recorded correctly. Various failures may occur in the device.

  For this reason, conventionally, there has been proposed a technique for grasping the type of an objective lens arranged in an optical path for an optical disk apparatus having a plurality of objective lenses and switching the objective lens. For example, in Patent Document 1, a permanent magnet supported by a fixed member and a Hall element supported by a movable member holding an objective lens are provided so as to face each other, and the Hall element is provided depending on the type of the selected objective lens. The configuration is such that the magnetic flux passing therethrough is changed, and thereby the type of the objective lens arranged in the optical path is detected.

  In Patent Document 2, in order to discriminate between the types of the first objective lens and the second objective lens, reflecting means is disposed at a predetermined position of the lens holder that holds the objective lens, and the first objective lens is in the optical path. A detecting means which is arranged at a predetermined position of the lens holder support so as to face the reflecting means when disposed inside, and emits light and receives reflected light from the reflecting means caused by the light emission. Proposed configuration.

Further, Patent Document 3 proposes a technique for discriminating the type of objective lens in the optical path by utilizing the fact that the amount of reflected light from the optical recording medium differs depending on the type of objective lens arranged in the optical path. Has been.
JP-A-9-305980 JP 10-198969 A JP 2003-99958 A

  However, when the type of the objective lens arranged in the optical path is determined using the configurations of Patent Document 1 and Patent Document 2, it is necessary to provide a new detection device to determine the type of the objective lens. In addition, there are problems such as an increase in cost and an increase in the weight of the movable member that enables the objective lens to move.

  Further, when the type of the objective lens arranged in the optical path is determined using the configuration of Patent Document 2, there is no need to newly provide a detection device as in Patent Document 1 and Patent Document 2, As a result of variations in the reflectance of the optical recording medium due to variations in the optical recording medium at the time of manufacture or the like, there is a problem that the type of the objective lens is erroneously determined.

  In view of the above problems, an object of the present invention is to provide a plurality of types of objective lenses, and in an optical disc apparatus that switches and uses objective lenses according to the type of optical recording medium, without providing a new detection device. An object of the present invention is to provide an optical disc apparatus capable of preventing erroneous setting of an objective lens arranged in an optical path. Another object of the present invention is to determine the type of objective lens that can accurately determine the type of objective lens arranged in the optical path without providing a new detection device in an optical pickup having a plurality of types of objective lenses. Is to provide a method.

To achieve the above object, the present invention includes a plurality of light sources that emit light beams having different wavelengths, a plurality of objective lenses that condense the light beams emitted from the light sources onto a recording surface of an optical recording medium, depending on the type of the optical recording medium, moving from the plurality of objective lenses and an objective lens switching means for selecting one arranged in the optical path, the objective lens disposed in the optical path in the optical axis direction A focus adjustment means for adjusting the focal position, a light detection means for receiving reflected light reflected by the recording surface and converting it into an electrical signal, a spherical aberration disposed between the light source and the objective lens. and the spherical aberration correcting element for correcting the, in the optical disc apparatus comprising a storage unit for storing information, a light beam emitted from the light source, the objective lens disposed in the optical path to the focus adjusting means From the S-shaped waveform of the focus error signal obtained by moving in the optical axis direction, the amplitude acquisition unit for acquiring the amplitude and the control amount of the spherical aberration correction element are switched to a predetermined plurality of control values, In the case of a control value, the amplitude of the S-shaped waveform is acquired from the amplitude acquisition unit, and the amplitude of the S-shaped waveform obtained in the case of a predetermined control value among the control values is acquired to be a constant value. Normalizing the amplitude of the S-shaped waveform, calculating an inclination of an approximate line indicating a relationship between the control amount and the amplitude of the normalized S-shaped waveform, and storing the inclination of the approximate line in advance in the storage unit. And a discriminating section for discriminating the type of the objective lens arranged in the optical path by comparison with the stored threshold value.

In order to achieve the above object, the present invention provides a plurality of light sources that emit light beams having different wavelengths, and a plurality of objective lenses that condense the light beams emitted from the light sources onto the recording surface of the optical recording medium. And a spherical aberration correction element that is disposed between the light source and the objective lens and corrects spherical aberration, and a storage unit that stores information, according to the type of the optical recording medium, In an optical disc apparatus that selects and uses one objective lens arranged in an optical path from a plurality of objective lenses, the objective lens arranged in the optical path by emitting a light beam from the light source is arranged in an optical axis direction. In the case of each control value, the amplitude acquisition unit for acquiring the amplitude from the S-shaped waveform of the focus error signal obtained by moving to and the control amount of the spherical aberration correction element are switched to a plurality of predetermined control values. The acquired amplitude of S shaped waveform from the amplitude obtaining portion, wherein the amplitude of the change rate of the S-shaped waveform to a change in the control amount, the are arranged in the optical path on the basis that depends on the type of the objective lens And a discriminator for discriminating the type of the objective lens.

According to the present invention, in the optical disc apparatus configured as described above, the determination unit determines the amplitude of the acquired S-shaped waveform as the amplitude of the S-shaped waveform obtained when the control value is a predetermined control value. Is normalized so as to be a constant value, and an inclination of an approximate line indicating the relationship between the control amount and the amplitude of the normalized S-shaped waveform is calculated and stored in advance in the storage unit and the inclination of the approximate line. The type of the objective lens arranged in the optical path is determined by comparison with the threshold value.

In order to achieve the above object, the present invention provides a plurality of light sources that emit light beams having different wavelengths, and a plurality of objective lenses that condense the light beams emitted from the light sources onto the recording surface of the optical recording medium. And a spherical aberration correction element that is arranged between the light source and the objective lens and corrects spherical aberration, and depending on the type of the optical recording medium, an optical path from among the plurality of objective lenses A discriminating method for discriminating the type of an objective lens arranged in the optical path of an optical pickup that selects and uses one objective lens arranged therein , wherein a control amount of the spherical aberration correction element is set to a predetermined value switching a plurality of control values, for the case of the control value, and emits a light beam from the light source, the objective lens disposed in the optical path by the focus adjustment unit by moving the optical axis direction Obtaining the S-shaped waveform of the focus error signal and obtaining the amplitude thereof, and obtaining the amplitude of the S-shaped waveform obtained in the case of a predetermined control value among the control values so as to be a constant value Normalizing the amplitude of the S-shaped waveform, calculating an inclination of an approximate line indicating the relationship between the control amount and the amplitude of the normalized S-shaped waveform, and predetermining the inclination of the approximate line. Determining the type of the objective lens arranged in the optical path by comparison with the determined threshold value.

  According to the first configuration of the present invention, the type of the objective lens is discriminated by utilizing the spherical aberration depending on the design of the objective lens. By using a member provided in the optical disk apparatus, it is possible to easily provide an optical disk apparatus that can determine the type of the objective lens without being affected by variations in the reflectance of the optical recording medium. For this reason, in an optical disc apparatus provided with a plurality of types of objective lenses and used by switching the objective lens according to the type of optical recording medium, an erroneous setting of the objective lens arranged in the optical path without providing a new detection device It is easy to realize an optical disc apparatus that can prevent the above.

  Further, according to the second configuration of the present invention, it is possible to determine the type of the objective lens without providing a separate detection device. In addition, since the discriminating unit is configured to discriminate the type of the objective lens using spherical aberration that depends on the design of the objective lens, the type of the objective lens is not affected by variations in the reflectance of the optical recording medium. Can be determined. Therefore, in an optical disc apparatus that includes a plurality of types of objective lenses and switches the objective lens according to the type of the optical recording medium, an erroneous setting of the objective lens arranged in the optical path can be performed without providing a new detection device. It is possible to provide an optical disc device that can be prevented.

  According to the third configuration of the present invention, in the optical disc apparatus having the second configuration, an optical disc apparatus that can easily prevent erroneous setting of the objective lens arranged in the optical path from the optical disc apparatus having the conventional configuration. It becomes possible to provide.

  Further, according to the fourth configuration of the present invention, since it is a configuration for determining the type of the objective lens using the spherical aberration correction element provided in the optical pickup, it is not necessary to provide a separate detection device, It is possible to determine the type of the objective lens without being affected by variations in the reflectance of the optical recording medium. Therefore, it is possible to provide a method for discriminating the type of objective lens that can accurately discriminate the type of objective lens arranged in the optical path without providing a new detection device in an optical pickup including a plurality of types of objective lenses.

  Hereinafter, the content of the present invention will be described in detail with reference to the drawings. However, the embodiment shown here is an example, and the present invention is not limited to the embodiment shown here.

(Configuration of optical disk device)
First, the configuration of the optical disc apparatus of the present embodiment will be described. FIG. 1 is a block diagram showing the configuration of the optical disc apparatus of the present embodiment. The optical disc apparatus 1 is provided so as to be able to reproduce information on an optical recording medium (optical disc) 15 and record information on the optical disc 15. The types of the optical disk 15 that can be recorded and reproduced by the optical disk apparatus 1 are CD, DVD, and BD.

  Reference numeral 2 denotes a spindle motor, and the optical disk 15 is detachably held by a chuck portion (not shown) provided on the spindle motor 2. Then, when recording / reproducing information on the optical disk 15, the spindle motor 2 continuously rotates the optical disk 15. The rotation control of the spindle motor 2 is performed by the spindle motor control unit 3.

  Reference numeral 4 denotes an optical pickup that irradiates the optical disc 15 with laser light emitted from a light source, thereby enabling writing of information on the optical disc 15 and reading of information recorded on the optical disc 15. FIG. 2 is a schematic diagram showing an optical system of the optical pickup 4. As shown in FIG. 2, the optical pickup 4 includes a first light source 21, a second light source 22, a color synthesis prism 23, a collimator lens 24, a beam splitter 25, a spherical aberration correction element 26, and an objective lens 27. And a condensing lens 29 and a photodetector 30. The configuration of the optical system that constitutes the optical pickup is not limited to this, and various changes can be made.

  The first light source 21 and the second light source 22 are both laser diodes (LDs), but the first light source 21 is a light source corresponding to BD, and emits laser light having a wavelength of, for example, 405 nm. On the other hand, the second light source 22 is a two-wavelength integrated LD and is a light source corresponding to a CD and a DVD. For example, a laser beam having a wavelength of 780 nm (laser light for CD) and a laser beam having a wavelength of 650 nm (DVD) Laser beam).

  In the optical pickup 4, the laser light emitted from the light sources 21 and 22 passes through a color synthesis prism 23 having the same optical axis of the laser light emitted from the first light source 21 and the second light source 22, and then a collimating lens. 24 becomes parallel light, passes through the beam splitter 25, and its details are corrected for spherical aberration by a spherical aberration correction element 26, which will be described later, and then focused on a recording surface 15 a on which information on the optical disk 15 is recorded by an objective lens 27. Is done. The optical pickup 4 is configured to switch between two types of an objective lens for CD / DVD used when recording and reproducing CD and DVD and an objective lens for BD used when recording and reproducing BD. However, this point will be described later.

  The reflected light reflected by the recording surface 15 a passes through the objective lens 27 and the spherical aberration correction element 26 in this order, is reflected by the beam splitter 25, and is collected on the light receiving unit of the photodetector 30 by the condenser lens 29. The photodetector 30 converts optical information contained in the received light beam into an electrical signal.

  Returning to FIG. 1, the slide motor control unit 5 controls the drive of a slide motor (not shown) provided so that the optical pickup 4 can move, and thereby the movement of the optical pickup 4 in the radial direction is controlled.

  The RF signal processing unit 6 processes the RF signal obtained by the photodetector 30 (see FIG. 2) of the optical pickup 4 and supplies the processed signal to the demodulation unit 7.

  The demodulator 7 demodulates the data, detects an error in the data, performs data correction processing if correction is possible when the error is detected, and supplies the reproduction data to the interface unit 8. When a reproduction error that cannot be corrected occurs, data is re-read (retry) by a known method.

  The interface unit 8 outputs the reproduction data supplied from the demodulation unit 7 to an external device such as a personal computer (not shown).

  The focus error signal processing unit 9 generates a focus error signal using a signal detected by the photodetector 30 of the optical pickup 4. The photodetector 30 has detection surfaces A, B, C, and D that are divided into four as shown in FIG. 2, and the difference (A + C) − () in the diagonal sum of the detection signals from the detection surfaces A to D. B + D) to generate a focus error signal. The focus error signal generated by the focus error signal processing unit 9 can be supplied to an actuator control unit 11 and an amplitude acquisition unit 13 described later in detail.

  The tracking error signal processing unit 10 generates a tracking error signal using a signal detected by the photodetector 30 of the optical pickup 4. The tracking error signal is generated by the difference (A + B) − (C + D) of the right and left sum of the detection signals from the detection surfaces A to D (see FIG. 2) of the photodetector 30. The tracking error signal generated by the tracking error signal processing unit 10 can be supplied to the actuator control unit 11.

  In the present embodiment, the focus error signal and the tracking error signal are obtained by dividing the detection surface of the photodetector 30 into four. However, the configuration for obtaining the focus error signal and the tracking error signal is limited to this. Various modifications are possible without departing from the scope of the present invention. That is, for example, the focus error signal may be obtained by a so-called spot size method, and the tracking error signal may be obtained by a so-called collect far field method.

  Based on the signals sent from the focus error signal processing unit 9 and the tracking error signal processing unit 10, the actuator control unit 11 supplies a drive signal to an actuator 28 (see FIG. 2) on which the objective lens 27 is mounted. To do. The actuator 28 to which the drive signal is supplied operates each part based on the signal, and moves the objective lens 27 in a focus direction parallel to the optical axis direction to adjust the focus. Tracking control is performed in which the laser beam spot position is adjusted to the track position formed on the optical disk 15 by moving in a direction parallel to the radial direction.

  The actuator control unit 11 moves the objective lens 27 in the focus direction (direction approaching the optical disc 15 or away from the optical disc 15) to obtain an S-shaped waveform of the focus error signal, or the objective lens described later. The actuator 28 is also controlled at the time of switching.

  Here, the configuration of the actuator 28 on which the objective lens 27 is mounted will be described with reference to FIGS. 3 and 4. 3 is a schematic plan view showing the configuration of the actuator 28, and FIG. 4 is a schematic cross-sectional view taken along the line AA in FIG.

  The actuator 28 holds the act base 40, the slide shaft 41 erected in the direction perpendicular to the act base 40, the CD / DVD objective lens 27 a and the BD objective lens 27 b, and the slide shaft 41. A lens holder 42 slidably supported on the actuator base 40, two yokes 43 standing on the act base 40, and two permanent magnets 44 standing on the inside of the yoke 43 on the act base 40. . The act base 40, the sliding shaft 41, and the yoke 43 are made of a magnetic material such as steel so that a magnetic path can be formed.

  A focusing coil 46 and a plate-like magnetic piece 47 are bonded and held on the lower side of the lens holder 42. The presence of the magnetic piece 47 makes it possible to keep the lens holder 42 in the levitated neutral position even when the control current flowing through the focusing coil 46 is interrupted, so that the objective lenses 27a and 27b Lens shift sensitivity is improved.

  The focus coil 46 is wound around the slide shaft 41 on the lower side of the magnetic piece 47 and is joined and held to the lens holder 42. When a current is passed through the focus coil 46, the lens holder 42 is energized. The lens is caused by the interaction between the magnetic flux generated by the pair of permanent magnets 44 arranged so as to sandwich the focusing coil 46 and the magnetic flux generated by energizing the focusing coil 46. The holder 42 moves in the focus direction. For this reason, the focus control of the objective lenses 27a and 27b can be performed.

  A tracking coil 45 formed in a rectangular shape is provided on the side surface of the lens holder 42 facing the permanent magnet 44 so as to be substantially symmetric with respect to the sliding shaft 41. Further, the tracking coil 45 is disposed so as to protrude from a position sandwiched between the opposing permanent magnets 45 so that a part of the tracking coil 45 is hardly affected by the magnetic force of the permanent magnets 44. By arranging in this way, the rotational moment acting on the lens holder 42 can be increased.

  When a current is passed through the tracking coil 45, the lens holder 42 is centered on the sliding shaft 41 due to the interaction between the magnetic flux generated by the permanent magnet 44 and the magnetic flux generated by energizing the tracking coil 45. Rotate. Therefore, the tracking control of the objective lenses 27a and 27b can be performed, and furthermore, the objective lenses 27a and 27b arranged in the optical path of the optical pickup 4 can be switched by rotating the lens holder 42 by 180 degrees. .

  That is, the actuator 28 serves as a focus adjustment unit that performs focus adjustment of the objective lenses 27a and 27b and a tracking adjustment unit that performs tracking adjustment, and further as an objective lens switching unit that switches between the objective lenses 27a and 27b disposed in the optical path. Function.

  Returning to FIG. 1, the spherical aberration correction element control unit 12 controls a spherical aberration correction element 26 (see FIG. 2) configured by a liquid crystal element. Here, the configuration of the spherical aberration correction element 26 will be described. 5A and 5B are diagrams for explaining the configuration of the spherical aberration correction element 26 according to the present embodiment. FIG. 5A is a schematic cross-sectional view showing the configuration of the spherical aberration correction element 26, and FIG. 3 is a schematic plan view showing a configuration of a transparent electrode 32a constituting the aberration correction element 26. FIG.

  The spherical aberration correction element 26 includes a liquid crystal 31, two transparent electrodes 32a and 32b that sandwich the liquid crystal 31, and two transparent substrates 33 that sandwich a portion formed by the liquid crystal 31 and the transparent electrodes 32a and 32b. ing. The transparent electrode 32a constituting the spherical aberration correction element 26 is divided into a plurality of concentric regions, while the transparent electrode 32b facing the transparent electrode 32a is not divided and becomes one common electrode as a whole. ing.

  When a driving voltage is applied to the transparent electrodes 32 a and 32 b of the aberration correction element 26 configured in this way, the liquid crystal 31 changes its orientation direction to cause a change in refractive index, and light that passes through the spherical aberration correction element 26. The beam causes a phase difference according to the drive voltage applied to the spherical aberration correction element 26. Since the transparent electrode 32a of the spherical aberration correction element 26 is divided into a plurality of parts as described above, the voltage applied to each region is adjusted to pass through the spherical aberration correction element 26. It is possible to generate a desired phase difference with respect to the light beam and appropriately correct spherical aberration. Note that the transparent electrodes 32a and 32b are electrically connected to the spherical aberration correction element control unit 12 by wires (not shown), and the applied drive voltage is controlled.

  In this embodiment, a liquid crystal element is used as the spherical aberration correction element 26. However, the present invention is not limited to this configuration, and a configuration using a beam expander as the spherical aberration correction element 26 may be used. Absent.

  Returning to FIG. 1, the amplitude acquisition unit 13 receives the S-shaped waveform information of the focus error signal from the focus error signal processing unit 9 and acquires the amplitude of the S-shaped waveform. The amplitude of the S-shaped waveform obtained here is supplied to the determination unit 14 described later.

  The determination unit 14 can determine whether the objective lens 27 disposed in the optical path of the optical pickup 4 is the CD / DVD objective lens 27a or the BD objective lens 27b. The discriminating unit 14 can give a command to the spherical aberration correction element control unit 12 to control the drive voltage applied to the spherical aberration correction element 26 and can also control the amplitude of the S-shaped waveform acquired by the amplitude acquisition unit 13. Is configured to receive. Details of a method for discriminating the type of the objective lens 27 by the discriminating unit 14 configured as described above will be described later.

  In addition, the overall control unit 17 includes a spindle motor control unit 3, a slide motor control unit 5, an RF signal processing unit 6, a demodulation unit 7, an interface unit 8, a focus error signal processing unit 9, a tracking error signal processing unit 10, and an actuator control. The entire apparatus is controlled by controlling the unit 11, the spherical aberration correction element control unit 12, the amplitude acquisition unit 13, the determination unit 14, and the storage unit 16 that stores information necessary for control.

(Objective lens type identification method)
Next, in the optical disc apparatus 1 configured as described above, whether the objective lens 27 disposed in the optical path of the optical pickup 4 is the CD / DVD objective lens 27a or the BD objective lens 27b. A determination method for determination will be described. FIG. 6 is a flowchart showing a procedure for determining the type of the objective lens 27 in the optical disc apparatus 1. Hereinafter, description will be given according to this flowchart.

  The type of the objective lens 27 arranged in the optical path of the optical pickup 4 is determined by, for example, turning on the power source of the optical disc apparatus 1 or changing the type of the objective lens 27 from the CD / DVD objective lens 27a to the BD objective lens 27b. This is started when switching to, and vice versa.

  When discrimination of the type of the objective lens 27 arranged in the optical path of the optical pickup 4 is started, first, N = 0 is set, and this is stored in the storage unit 16 (see FIG. 1) (step S1). Next, according to a command from the determination unit 14 (see FIG. 1), the spherical aberration correction element control unit 12 (see FIG. 1) sets the spherical aberration correction element 26 (see FIG. 2) to a predetermined control value (step). S2). When the spherical aberration correction element 26 is set to a predetermined control value, a DVD laser beam is emitted from the second light source 22 (see FIG. 2) (step S3). The type of laser light emitted here is not particularly limited, and may be CD laser light or BD laser light.

  Next, the actuator 28 is moved in a direction in which the objective lens 27 approaches the optical disk 15 (a direction away from the optical disk 15 may be in the focus direction), and an S-shaped waveform of the focus error signal is detected (step). S4). Here, since the detection level of the S-shaped waveform varies depending on the difference in reflectance of the optical disc 15, gain setting is performed so that a good S-shaped waveform is detected (step S5).

  When the gain setting is performed, the amplitude acquisition unit 13 acquires the amplitude of the S-shaped waveform (hereinafter, sometimes referred to as “S-shaped amplitude”), and the acquired amplitude is stored in the storage unit 16 (Step S1). S6).

  Next, 1 is added to the value of N according to the formula N = N + 1 (step S7), and the spherical aberration correction element control unit 12 drives the spherical aberration correction element 26 according to a command from the determination unit 14 (control). (Amount) is changed by a predetermined amount (step S8). Then, with the control value of the spherical aberration correction element 26 being different from the previous one, the amplitude acquisition unit 13 acquires the S-shaped amplitude, and the acquired amplitude is stored in the storage unit 16 (step S9).

  Next, it is confirmed by the determination part 14 whether N is smaller than 2 (step S10). If N is smaller than 2, steps S7 to S10 are further repeated. That is, in the present embodiment, the S-shaped amplitude is acquired for three cases where the control values for controlling the spherical aberration correction element 26 are different.

  When N is 2 or more, the three acquired S-shaped amplitudes are normalized so that the first acquired S-shaped amplitude (corresponding to the S-shaped amplitude obtained in step S6) is a constant value. (Step S11). Note that, here, the acquired three S-shaped amplitude values are each divided by the first acquired S-shaped amplitude value.

  In this embodiment, normalization is performed so that the initially acquired S-shaped amplitude becomes a constant value, but instead of normalizing so that the initially acquired S-shaped amplitude becomes a constant value, 2 The configuration may be such that normalization is performed so that the S- or third-acquired S-shaped amplitude becomes a constant value.

  Next, from the control value of the spherical aberration correcting element 26 and the normalized three S-shaped amplitudes, an inclination of an approximate line indicating the relationship between the control amount of the spherical aberration correcting element and the S-shaped amplitude is calculated (step). S12). Note that the slope of the approximate straight line obtained here is not affected by variations in the reflectance of the optical disk 15 because the S-shaped amplitude normalized in step S11 is used.

  Here, FIG. 7 is a graph (solid line and broken line) conceptually showing the relationship between the control amount of the spherical aberration correcting element and the normalized S-shaped amplitude, and the black plot and its approximate straight line shown in the figure are When the control value of the spherical aberration correction element 26 is switched, the S-shaped amplitude changes when the CD / DVD objective lens 27a is arranged in the optical path and the BD objective lens 27b is arranged. It is shown about the case.

  As shown in FIG. 7, when the amount of control of the spherical aberration correction element 26 is changed, the objective lens 27a of the CD / DVD objective lens 27a is when the BD objective lens 27b is arranged in the optical path. It can be seen that the S-shaped amplitude is greatly changed (easily affected by the influence of spherical aberration), and the inclination of the approximate straight line is increased, compared to the case where is arranged. Therefore, if a threshold line as shown in FIG. 7 is obtained in advance by experiments or the like so that the CD / DVD objective lens 27a and the BD objective lens 27b can be distinguished, the slope of the threshold line is set as a threshold value. It is possible to determine the type of the objective lens 27 arranged in the optical path.

  Accordingly, it is confirmed whether or not the inclination of the approximate line obtained in step S16 is larger than the threshold value stored in the storage unit 16 in advance (step S17). 27 is determined as the BD objective lens 27a (step S18), and when the inclination of the approximate line is smaller than the threshold value, the objective lens 27 is determined as the CD / DVD objective lens 27b (step S19).

  As described above, the optical disc apparatus 1 can accurately determine the type of the objective lens 27 arranged in the optical path. For this reason, since the optical disk apparatus 1 can arrange an appropriate objective lens 27 in the optical path based on the result determined by the determination unit 14, an erroneous setting of the objective lens can be prevented.

  In the present embodiment, the control value of the spherical aberration correction element 26 is switched at three points, and the type of the objective lens is discriminated from the change of the S-shaped amplitude at these three points. The value may be switched as long as it is two or more. However, if the number of switching points is small, there is a possibility of misjudgment, and if there are too many switching points, there is a problem that it takes a long time to make a decision. preferable.

  As for the control value of the spherical aberration correction element 26 to be switched when the type of the objective lens is discriminated, for example, when the control value is selected so as to sandwich the apex of the parabola shown by the solid line in FIG. 7, an accurate approximate straight line is obtained. Care must be taken in selecting the control value.

  Further, in the present embodiment, it is configured to discriminate between two types of objective lenses, a CD / DVD objective lens and a BD objective lens, but the present invention is also capable of discriminating types of objective lenses other than these two types. Of course, it is applicable. The present invention can also be applied to the case where the types of three or more types of objective lenses are discriminated. In this case, instead of comparing the size with one threshold as in the present embodiment, a plurality of threshold values are obtained in advance, and the type of the objective lens is determined by the size comparison with the plurality of thresholds. It becomes.

  In addition, in this embodiment, the objective lens is switched using an actuator that performs focus control and tracking control. However, when an objective lens switching is provided by separately providing an objective lens switching actuator. However, the objective lens type discrimination method of the present invention can of course be applied.

  According to the present invention, in an optical disc apparatus having a plurality of objective lenses, it is possible to accurately determine the type of objective lens, thereby preventing erroneous setting of the objective lens. Therefore, it is useful for an optical disc apparatus having a plurality of objective lenses.

These are block diagrams which show the structure of the optical disk apparatus of this embodiment. These are the schematic diagrams which show the optical system of the optical pick-up with which the optical disk apparatus of this embodiment is provided. These are the schematic plan views which show the structure of the actuator which mounts the objective lens with which the optical disk apparatus of this embodiment is provided. These are schematic sectional drawing at the time of cutting in the position of the AA line of FIG. These are the figures explaining the structure of the aberration correction element with which the optical disk apparatus of this embodiment is provided. These are the flowcharts which showed the procedure which discriminate | determines the kind of objective lens in the optical disk device of this embodiment. These are graphs conceptually showing the relationship between the control amount of the spherical aberration correcting element and the normalized S-shaped amplitude.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk apparatus 4 Optical pick-up 13 Amplitude acquisition part 14 Discriminating part 21 1st light source 22 2nd light source 26 Spherical aberration correction element 27 Objective lens 28 Actuator (Objective lens switching means, focus adjustment means)
30 photodetector (light detection means)

Claims (4)

A plurality of light sources that emit light beams having different wavelengths;
A plurality of objective lenses for condensing the light beam emitted from the light source on the recording surface of the optical recording medium;
According to the type of the optical recording medium, objective lens switching means for selecting one of the plurality of objective lenses and arranging it in the optical path;
Focus adjusting means for adjusting the focal position by moving the objective lens arranged in the optical path in the optical axis direction;
Light detecting means for receiving reflected light reflected by the recording surface and converting it into an electrical signal;
A spherical aberration correction element that is disposed between the light source and the objective lens and corrects spherical aberration;
A storage unit for storing information;
In an optical disc device comprising:
A light beam is emitted from the light source, and the amplitude is obtained from the S-shaped waveform of the focus error signal obtained by moving the objective lens arranged in the optical path in the optical axis direction by the focus adjusting means. An amplitude acquisition unit;
The control amount of the spherical aberration correction element is switched to a predetermined plurality of control values, and for each control value, the amplitude of the S-shaped waveform is acquired from the amplitude acquisition unit, and a predetermined control value among the control values The amplitude of the S-shaped waveform acquired so that the amplitude of the S-shaped waveform obtained in the above case becomes a constant value is normalized, and the relationship between the control amount and the amplitude of the normalized S-shaped waveform is shown. A determination unit that calculates an inclination of the approximate line and determines a type of the objective lens arranged in the optical path by comparing the inclination of the approximate line and a threshold value stored in the storage unit in advance;
An optical disc apparatus comprising: A plurality of light sources that emit light beams having different wavelengths;
A plurality of objective lenses for condensing the light beam emitted from the light source on the recording surface of the optical recording medium;
A spherical aberration correction element that is disposed between the light source and the objective lens and corrects spherical aberration;
A storage unit for storing information;
In an optical disc apparatus that uses one objective lens arranged in an optical path from among the plurality of objective lenses according to the type of the optical recording medium,
An amplitude acquisition unit for acquiring the amplitude from an S-shaped waveform of a focus error signal obtained by emitting a light beam from the light source and moving the objective lens arranged in the optical path in the optical axis direction;
The control amount of the spherical aberration correction element is switched to a predetermined plurality of control values, and for each control value, the amplitude of the S-shaped waveform is acquired from the amplitude acquisition unit, and the S-shaped waveform with respect to the change in the control amount is acquired. A discriminating unit for discriminating the type of the objective lens arranged in the optical path based on the change rate of the amplitude depending on the type of the objective lens;
An optical disc apparatus comprising: The determination unit normalizes the acquired amplitude of the S-shaped waveform so that the amplitude of the S-shaped waveform obtained in the case of a predetermined control value among the control values becomes a constant value, and the control amount And the slope of the approximate straight line indicating the relationship between the normalized S-wave waveform amplitude and the slope of the approximate straight line and a threshold value stored in advance in the storage unit . The optical disc apparatus according to claim 2, wherein the type of the objective lens is discriminated. A plurality of light sources that emit light beams having different wavelengths;
A plurality of objective lenses for condensing the light beam emitted from the light source on the recording surface of the optical recording medium;
A spherical aberration correction element that is disposed between the light source and the objective lens and corrects spherical aberration;
The provided, depending on the type of the optical recording medium, the plurality of objective lenses are arranged the objective lens in the optical path of one selected and an optical pickup used which is arranged in the optical path from the objective lens A determination method for determining the type of
The control amount of the spherical aberration correction element is switched to a plurality of predetermined control values, and for each control value, a light beam is emitted from the light source, and the objective lens arranged in the optical path is moved to the focus adjusting means. Obtaining an S-shaped waveform of the focus error signal by moving in the direction of the optical axis by acquiring the amplitude thereof;
Normalizing the amplitude of the S-shaped waveform acquired so that the amplitude of the S-shaped waveform obtained in the case of a predetermined control value among the control values is a constant value;
Calculating an inclination of an approximate line indicating a relationship between the control amount and the amplitude of the normalized S-shaped waveform;
Determining the type of the objective lens arranged in the optical path by comparing the inclination of the approximate straight line with a predetermined threshold value;
A method for discriminating the type of objective lens.

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